Method of manufacturing a spherical annular seal

ABSTRACT

A spherical annular seal having a through hole in a center thereof and a partially convex spherical surface portion on an outer surface thereof, wherein an inner peripheral surface of the spherical annular seal defining the through hole is reinforced by a reinforcing member formed of a metal mesh, and a uniform lubricating sliding layer of a lubricating composition containing 70 to 90 wt. % of boron nitride and 10 to 30 wt. % of alumina is formed on a surface of the partially convex spherical surface portion.

This is a divisional of application Ser. No. 08/130,898, filed Oct. 4,1993.

BACKGROUND OF THE INVENTION

The present invention relates to a spherical annular seal used in aspherical pipe joint for an automobile exhaust pipe and a method ofmanufacturing the same.

Conventionally, a spherical annular seal for use in a spherical pipejoint for an automobile exhaust pipe, in which a mixture of relativelyshort fibers (2 to 8 mm) and a solid lubricant such as graphite iscompression-formed, is known, as disclosed in, for instance, U.S. Pat.No. 4,659,091 (hereafter referred to as the prior art publication 1).

Although the seal disclosed in this prior art publication 1 has theadvantage that it can be manufactured easily at low cost, the seal has adrawback in that stick slip often generating abnormal noise can beinduced in friction with a mating member. Also, the seal has a problemin that, owing to problems with materials constituting the seal and witha method of manufacturing the seal, the strength of the seal comes todecline over periods of use, possibly resulting in partial fracture orbreakage of thee seal and thereby lowering the function of the seal.

The seal in accordance with the prior art publication 1 has a sphericalannular shape, and is provided with a through hole in its center and apartially convex spherical surface portion on its outer side. Therefore,particularly at the time of manufacturing the seal, portions filledcoarsely with material and other portions filled densely with materialcan occur in a small-diameter portion (a tip portion of the seal) of thepartially convex spherical surface portion of the seal. In that case,pressure cannot be applied sufficiently to the coarsely filled portionsduring subsequent compression forming, so that an insufficient-strengthportion may occur in that portion. The insufficient-strength portionpossibly leads to fracture or breakage of that portion during the use ofthe seal, causing leakage of exhaust gases.

Accordingly, in view of the problem of a decline in the strength of theseal in accordance with the above-described prior art publication 1 andthe problem of occurrence of abnormal noise during an initial period offriction with the mating member, a seal disclosed in Japanese PatentUnexamined Publication No. 215916/1990 (hereafter referred to as theprior art publication 2) has been proposed.

Namely, the seal proposed in the prior art publication 2 is arrangedsuch that a mixture including a solid lubricant, such as graphite, metalfibers 10 to 200 μm in diameter and 100-800μm in length, and a resinbinder is so compressed together with a tubular reinforcing memberformed of a metal mesh that the mixture is filled in mesh openings ofthe tubular reinforcing member and surrounds the reinforcing member, athrough hole with the reinforcing member exposed being formed in itscenter and a partially convex spherical surface portion being formed onits outer surface, wherein a lubricating sliding layer includingtetrafluoroethylene or a lubricating composition havingtetrafluoroethylene as a main component is formed on the partiallyconvex spherical surface portion of the seal.

In accordance with the prior art publication 2, it is possible to obtaina seal having enhanced strength without causing insufficiency instrength attributable to the coarse and dense filling of the material inthe small-diameter portion of the partially convex spherical surfaceportion, which is the drawback of the above-described prior artpublication 1. In addition, since the lubricating sliding layer isformed on the surface of the partially convex spherical surface portionwhich is a frictional surface in friction with a mating member, thedrawback of the occurrence of abnormal noise particularly during aninitial period of friction is not experienced. Thus, the problems of theseal in accordance with the prior art publication 1 are overcome.

It is true that the seal in accordance with the above-described priorart publication 2 overcomes the drawbacks of the seal disclosed in theprior art publication 1 according to the test conditions and test methoddisclosed in the publication 2. However, in a case where the seal isused under test conditions and a test method which are severer thanthose of the aforementioned test conditions and test method, therearises a new problem of an exfoliation or peeling taking place in thelubricating sliding layer formed on the partially convex sphericalsurface portion on its outer surface, resulting in the occurrence ofabnormal noise.

In particular, as for the spherical pipe joint used for the purpose ofattenuating vibrations transmitted from the automobile engine to theexhaust pipe, the position of its installation in the exhaust pipeextending from the engine to the muffler is determined by taking variousconditions into consideration. Accordingly, the seal which isincorporated in such a joint is required to be capable of coping withall the conditions.

SUMMARY OF THE INVENTION

The present invention has been accomplished in view of theabove-described problems, and an object of the present invention is toprovide a spherical annular seal in which a decline in a slidingcharacteristic and the occurrence of abnormal noise are prevented notonly during an initial period but over long periods of use withoutcausing an exfoliation in a lubricating sliding layer formed on apartially convex spherical surface portion on its outer surface, as wellas a method of manufacturing the same.

In accordance with one aspect of the present invention, the above-objectis attained by a spherical annular seal particularly used for an exhaustpipe joint, the spherical annular seal being formed by compressionforming a mixture of a solid lubricant, metal short fibers, and asynthetic resin binder, the spherical annular seal having a through holein a center thereof and a partially convex spherical surface portion onan outer surface thereof, wherein an inner peripheral surface of thespherical annular seal defining the through hole is reinforced by areinforcing member formed of a metal mesh, and a uniform lubricatingsliding layer of a lubricating composition containing 70 to 90 wt. % ofboron nitride and 10 to 30 wt. % of alumina and/or silica, or alubricating composition containing 100 parts by weight of thelubricating composition containing 70 to 90 wt. % of boron nitride and10 to 30 wt. % of alumina and/or silica and further containingpolytetrafluoroethylene in a proportion of 200 parts by weight or less,preferably ranging from 50 to 150 parts by weight, is formed on asurface of the partially convex spherical surface portion.

In accordance with another aspect of the present invention, theabove-object is attained by a spherical annular seal particularly usedfor an exhaust pipe joint, the spherical annular seal being formed bycompression forming a mixture of a solid lubricant, metal short fibers,and a synthetic resin binder, the spherical annular seal having athrough hole in a center thereof and a partially convex sphericalsurface portion on an outer surface thereof, wherein an inner peripheralsurface of the spherical annular seal defining the through hole isreinforced by a reinforcing member formed of a metal mesh, and a surfaceof the partially convex spherical surface portion is formed into asmooth surface in which a uniform lubricating sliding layer of alubricating composition containing 70 to 90 wt. % of boron nitride and10 to 30 wt. % of alumina and/or silica, or a lubricating compositioncontaining 100 parts by weight of the lubricating composition containing70 to 90 wt. % of boron nitride and 10 to 30 wt. % of alumina and/orsilica and further containing polytetrafluoroethylene in a proportion of200 parts by weight or less, preferably ranging from 50 to 150 parts byweight, and a reinforcing member formed of a metal mesh covering thelubricating sliding layer and integrated with the lubricating slidinglayer, are present in mixed form.

In accordance with still another aspect of the present invention, theabove-object is attained by a spherical annular seal particularly usedfor an exhaust pipe joint, the spherical annular seal being formed bycompression forming a mixture of a solid lubricant, metal short fibers,and a synthetic resin binder, the spherical annular seal having athrough hole in a center thereof and a partially convex sphericalsurface portion on an outer surface thereof, wherein an inner peripheralsurface of the spherical annular seal defining the through hole isreinforced by a reinforcing member formed of a metal mesh, and a surfaceof the partially convex spherical surface portion is formed into asmooth surface including a uniform lubricating sliding layer of alubricating composition containing 70 to 90 wt. % of boron nitride and10 to 30 wt. % of alumina and/or silica, or a lubricating compositioncontaining 100 parts by weight of the lubricating composition containing70 to 90 wt. % of boron nitride and 10 to 30 wt. % of alumina and/orsilica and further containing polytetrafluoroethylene in a proportion of200 parts by weight or less, preferably ranging from 50 to 150 parts byweight, and also including a reinforcing member extending integrallyfrom the reinforcing member for reinforcing the inner peripheral surfaceof the spherical annular seal, and integrated with and covering asmall-diameter end of the partially convex spherical surface portion andmixed in and integrated with the lubricating sliding layer on thepartially convex spherical surface portion.

In accordance with a further aspect of the present invention, theabove-object is attained by a method of manufacturing a sphericalannular seal, comprising the steps of: fitting a tubular reinforcingmember formed of a metal mesh over an outer peripheral surface of a coreof a die having a generally cylindrical hollow portion in its interior;forming a preform having the tubular reinforcing member on its innersurface by filling a mixture of a solid lubricant, metal short fibers,and a synthetic resin binder into the generally cylindrical hollowportion of the die in such a manner as to fill mesh openings of thetubular reinforcing member and cover the tubular reinforcing member, andby compression forming the mixture and the reinforcing member in adirection of a core axis; forming a coating layer constituted by alubricating composition by coating an outer peripheral surface of thepreform with an aqueous dispersion containing as a solid content 20 to50 wt. % of the lubricating composition containing 70 to 90 wt. % ofboron nitride and 10 to 30 wt. % of alumina and/or silica, or alubricating composition containing 100 parts by weight of thelubricating composition containing 70 to 90 wt. % of boron nitride and10 to 30 wt. % of alumina and/or silica and further containingpolytetrafluoroethylene in a proportion of 200 parts by weight or less,preferably ranging from 50 to 150 parts by weight, and by drying theaqueous dispersion; preparing a die having a partially concave sphericalsurface portion on its inner surface, and fitting the preform with thecoating layer of the lubricating composition formed thereon over anouter peripheral surface of the core of the die; compressing the preformin a direction of a core axis for obtaining a spherical annular memberwhich has in its center a through hole with its inner peripheral surfacereinforced by the compressed tubular reinforcing member, as well as apartially convex spherical surface portion on its outer surface, auniform lubricating sliding layer of the lubricating compositioncontaining 70 to 90 wt. % of boron nitride and 10 to 30 wt. % of aluminaand/or silica, or the lubricating composition containing 100 parts byweight of the lubricating composition containing 70 to 90 wt. % of boronnitride and 10 to 30 wt. % of alumina and/or silica and furthercontaining polytetrafluoroethylene in a proportion of 200 parts byweight or less, preferably ranging from 50 to 150 parts by weight, beingformed on a surface of the partially convex spherical surface portion;and placing the spherical annular member in a heating furnace to heatand cure the synthetic resin binder in the mixture.

In accordance with a still further aspect of the present invention, theabove-object is attained by a method of manufacturing a sphericalannular seal, comprising the steps of: fitting a tubular reinforcingmember formed of a metal mesh over an outer peripheral surface of a coreof a die having a generally cylindrical hollow portion in its interior;forming a preform having the tubular reinforcing member on its innersurface by filling a mixture of a solid lubricant, metal short fibers,and a synthetic resin binder into the generally cylindrical hollowportion of the die in such a manner as to fill mesh openings of thetubular reinforcing member and cover the tubular reinforcing member, andby compression forming the mixture and the reinforcing member in adirection of a core axis; forming a coating layer constituted by alubricating composition by coating an outer peripheral surface of thepreform with an aqueous dispersion containing as a solid content 20 to50 wt. % of the lubricating composition containing 70 to 90 wt. % ofboron nitride and 10 to 30 wt. % of alumina and/or silica, or alubricating composition containing 100 parts by weight of thelubricating composition containing 70 to 90 wt. % of boron nitride and10 to 30 wt. % of alumina and/or silica and further containingpolytetrafluoroethylene in a proportion of 200 parts by weight or less,preferably ranging from 50 to 150 parts by weight, and by drying theaqueous dispersion; preparing a die having a partially concave sphericalsurface portion on its inner surface, and fitting the preform with thecoating layer of the lubricating composition formed thereon over anouter peripheral surface of the core of the die, and fitting a tubularreinforcing member formed of a metal mesh over an outer peripheralsurface of the preform; compressing the preform and the tubularreinforcing member in a direction of a core axis for obtaining aspherical annular member which has in its center a through hole with itsinner peripheral surface reinforced by the compressed tubularreinforcing member, as well as a partially convex spherical surfaceportion on its outer surface, a surface of the partially convexspherical surface portion being formed into a smooth surface in which alubricating sliding layer of the lubricating composition containing 70to 90 wt. % of boron nitride and 10 to 30 wt. % of alumina and/orsilica, or the lubricating composition containing 100 parts by weight ofthe lubricating composition containing 70 to 90 wt. % of boron nitrideand 10 to 30 wt. % of alumina and/or silica and further containingpolytetrafluoroethylene in a proportion of 200 parts by weight or less,preferably ranging from 50 to 150 parts by weight, and the reinforcingmember formed of the metal mesh covering the lubricating sliding layerand integrated with the lubricating sliding layer are present in mixedform; and placing the spherical annular member in a heating furnace toheat and cure the synthetic resin binder in the mixture.

In accordance with a still further aspect of the present invention, theabove-object is attained by a method of manufacturing a sphericalannular seal, comprising the steps of: preparing a die having agenerally cylindrical hollow portion in its interior, filling the hollowportion with a mixture of a solid lubricant, metal short fibers, and asynthetic resin binder, and compression forming the mixture in adirection of a core axis so as to form a preform; forming a coatinglayer constituted by a lubricating composition by coating an outerperipheral surface of the preform with an aqueous dispersion containingas a solid content 20 to 50 wt. % of the lubricating compositioncontaining 70 to 90 wt. % of boron nitride and 10 to 30 wt. % of aluminaand/or silica, or a lubricating composition containing 100 parts byweight of the lubricating composition containing 70 to 90 wt. % of boronnitride and 10 to 30 wt. % of alumina and/or silica and furthercontaining polytetrafluoroethylene in a proportion of 200 parts byweight or less, preferably ranging from 50 to 150 parts by weight, andby drying the aqueous dispersion; preparing a reinforcing member formedof a metal mesh having an inner tubular portion, a curved portioncontinuing from the inner tubular portion, and an outer tubular portioncontinuing from the curved portion; inserting the preform with thecoating layer of the lubricating composition formed thereon between theinner and outer tubular portions of the reinforcing member formed of themetal mesh, and fitting an assembly of the preform and the reinforcingmember over an outer peripheral surface of the core of a die having apartially concave spherical surface portion on its inner surface so asto be located on the partially concave spherical surface portion of thedie; compression forming the assembly of the preform and the reinforcingmember in a direction of a core axis, for obtaining a spherical annularmember which has in its center a through hole with its inner peripheralsurface reinforced by the compressed tubular reinforcing member, as wellas a partially convex spherical surface portion on its outer surface, asurface of the partially convex spherical surface portion being formedinto a smooth surface in which a lubricating sliding layer of thelubricating composition containing 70 to 90 wt. % of boron nitride and10 to 30 wt. % of alumina and/or silica, or the lubricating compositioncontaining 100 parts by weight of the lubricating composition containing70 to 90 wt. % of boron nitride and 10 to 30 wt. % of alumina and/orsilica and further containing polytetrafluoroethylene in a proportion of200 parts by weight or less, preferably ranging from 50 to 150 parts byweight, and the reinforcing member extending from the through hole andintegrated with and covering a small-diameter end of the partiallyconvex spherical surface portion and the lubricating sliding layer onthe partially convex spherical surface portion are present in mixedform; and placing the spherical annular member in a heating furnace toheat and cure the synthetic resin binder in the mixture.

In the spherical annular seal in accordance with the present invention,a uniform lubricating sliding layer of a lubricating compositioncontaining boron nitride and alumina and/or silica, or a lubricatingcomposition containing boron nitride, alumina and/or silica, andpolytetrafluoroethylene, is formed on the surface of the partiallyconvex spherical surface portion forming a frictional surface withrespect to a mating member. Accordingly, when the spherical annular sealundergoes friction with respect to the mating member, relative angularmovement of upstream- and down-stream-side exhaust pipes is permitted atlow frictional torque without being affected by the conditions of use ofthe seal, and abnormal noise is prevented from occurring.

The exfoliation or peeling of the lubricating sliding layer from thepartially convex spherical surface portion does not occur since theretention of the lubricating sliding layer on the partially convexspherical surface portion of the seal is enhanced by alumina and/orsilica which is compounded with boron nitride at a fixed ratio, andsince the adhesion of the lubricating sliding layer formed of thelubricating composition containing polytetrafluoroethylene is enhancedby polytetrafluoroethylene.

Furthermore, in the seal in which the partially convex spherical surfaceportion of the seal comprises the lubricating sliding layer and thereinforcing member formed of a metal mesh integrated with the slidinglayer, since the sliding layer is reinforced by the reinforcing member,the aforementioned advantages appear more noticeably.

In the method of manufacturing a spherical annular seal in which thelubricating sliding layer and the reinforcing member formed of the metalmesh are integrated in mixed form, by using the reinforcing memberhaving an inner tubular portion, a curved portion continuing from theinner tubular portion, and an outer tubular portion continuing from thecurved portion, advantages are offered in that the manufacturing processis simplified, and that the small-diameter end of the partially convexspherical surface portion of the spherical annular seal can bereinforced.

Hereafter, a detailed description of the present invention will be givenof an embodiment of the spherical annular seal, specific examples ofcomponent materials of the spherical annular seal and a method ofmanufacturing the seal with reference to the accompanying drawings. Itshould be noted that the present invention is not restricted to thesespecific examples.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical cross-sectional view of an example of a sphericalannular seal in accordance with the present invention;

FIG. 2 is a vertical cross-sectional view of another example of aspherical annular seal in accordance with the present invention;

FIG. 3 is a vertical cross-sectional view of a still another example ofspherical annular seal in accordance with the present invention;

FIG. 4 is a vertical cross-sectional view of a die for fabricating apreform;

FIG. 5 is a vertical cross-sectional view illustrating a state in whichthe preform is fabricated;

FIG. 6 is a vertical cross-sectional view of the preform;

FIG. 7 is a vertical cross-sectional view of the preform coated with alubricating composition;

FIG. 8 is a vertical cross-sectional view illustrating a state in whicha spherical annular member is fabricated;

FIG. 9 is a vertical cross-sectional view of the spherical annularmember;

FIG. 10 is a vertical cross-sectional view illustrating a state in whichanother example of the spherical annular member is fabricated;

FIG. 11 is a vertical cross-sectional view of the other example of thespherical annular member;

FIG. 12 is a vertical cross-sectional view of a reinforcing member;

FIG. 13 is a vertical cross-sectional view of an assembly of thereinforcing member and the preform; and

FIG. 14 is a vertical cross-sectional view of an exhaust pipe jointincorporating the spherical annular seal.

DESCRIPTION OF THE PREFERRED EMBODIMENT

(Mixture)

(A) Metal Short Fibers

As metal short fibers, those obtained by cutting wool-like fibers formedby shaving iron or an iron alloy, such as steel and stainless steel,copper or a copper alloy, such as bronze, phosphur bronze, lead bronze,brass, and aluminum bronze, or by chipping raw wires formed of suchmaterials.

In particular, short fibers having a diameter of 10 to 200 μm and alength of 100 to 800 m are preferable since they permit a reinforcingmember and a mixture to be integrated firmly for the following reasons:These short fibers form a uniform mixture; they can be filled uniformlyin a die during the manufacture of the seal; they can be filled intomesh openings of the reinforcing member formed of a metal mesh whichwill be described later; and the fibers can be intertwined with eachother. As for the metal short fibers, iron-based or copper-based fiberscan be used singly or in the form of a mixture thereof.

(B) Solid Lubricant

As a solid lubricant, powder of graphite, molybdenum disulfide or thelike is used singly or in the form of a mixture thereof.

(C) Synthetic Resin Binder

As a synthetic resin binder, a phenol resin, a polyimide resin or thelike is used.

The aforementioned metal short fibers, solid lubricant, and syntheticresin binder are charged into a mixer, and are stirred and mixed so asto be formed into a uniform mixture. As compounding proportions of thismixture 50 to 75 wt. % of the metal short fibers, 15 to 30 wt. % of thesolid lubricant, and 5 to 25 wt. % of the synthetic resin binder arepreferable ranges of composition.

(Reinforcing Member)

As the reinforcing member, a metal mesh (wire net) formed by weaving orknitting fine wires of stainless steel or iron is used. In terms of theform of the reinforcing member, it is possible to use, for instance, thefollowing: (1) a tubular reinforcing member formed by convoluting ametal mesh, formed by weaving or knitting fine metal wires into a beltshape, by at least one turn into a tubular shape, and then by securingan overlapping portion by means of spot welding or a clasp; (2) anannular reinforcing member in which the tubular reinforcing member iscompressed in the axial direction of the cylinder; (3) a tubularreinforcing member constituted by a tubular woven metal mesh or in whichsuch tubular woven metal meshes are fitted one over another; (4) areinforcing member comprised of an inner tubular portion, a turned-backcurved portion continuing from the inner tubular portion, and an outertubular portion continuing from the curved portion, which are formed byturning back one end of a tubular woven metal mesh toward the other; and(5) a reinforcing member comprised of an inner tubular portion, aturned-back curved portion continuing from the inner tubular portion,and an outer tubular portion continuing from the curved portion, whichare formed such that a metal mesh, formed by weaving or knitting finemetal wires into a belt shape, is cut into a rectangular shape, thismaterial is folded in two, and is then convoluted into a tubular shape,and opposite ends are superposed one on top of the other and aretemporarily fixed.

As the wire diameter of the fine metal wire forming the metal wire net,a fine metal wire having a diameter of 0.10 to 0.31 mm or thereabouts isused, and a metal wire net whose mesh openings are 3 to 6 mm orthereabouts is suitably used.

(Preform)

The preform is formed by filling a die having a hollow cylindricalportion with a mixture of the above-described composition, and bysubjecting this mixture to compression forming in the axial direction ofthe hollow cylindrical portion. In terms of its configuration, thispreform has dimensional such relationships that its inside diameter islarger than the inside diameter of the spherical annular seal, i.e., afinal product, its outside diameter is smaller than the outside diameterof the seal, and its height is larger than the height of the seal. Ifthe operating efficiency is taken into consideration, a cylindricallyshaped member whose outer peripheral surface at one end portion thereofis tapered toward the end is preferable.

This preform may be fabricated as one which is provided with areinforcing member on its inner peripheral surface, by placing theabove-described tubular reinforcing member on its inner peripheralsurface in advance, filling the mixture in such a manner as to cover thereinforcing member, and then by performing compression forming.

Then, this preform is formed by subjecting the mixture in the hollowcylindrical portion of the die to compression forming under a pressureof 0.1 to 0.8 ton/cm².

(Lubricating Composition)

As a lubricating composition, an aqueous dispersion containing as asolid content 20 to 50 wt. % of a lubricating composition containing 70to 90 wt. % of boron nitride and 10 to 30 wt. % of alumina and/or silicais used. An alternative lubricating composition may be an aqueousdispersion which contains as a solid content 20 to 50 wt. % of alubricating composition in which a lubricating composition containing 70to 90 wt. % of boron nitride and 10 to 30 wt. % of alumina and/or silicais set as 100 parts by weight, and which additionally containspolytetrafluoro-ethylene in the proportion of 200 parts by weight orless, preferably 50 to 150 parts by weight.

The above-described aqueous dispersion of the lubricating composition iscoated on the outer peripheral surface of the above-described preform bymeans of brushing, spraying, or the like in the manufacturing methodwhich will be described later. In a final compression process, thecoating is spread into a uniform and very small thickness (10 to 300 μm)on the surface of a partially convex spherical portion of a sphericalannular seal so as to form a lubricating sliding layer.

In coating, in a case where the solid content in the aqueous dispersionis 20 to 30 wt. % (water content of 70 to 80 wt. %), a lubricatingsliding layer of a desired thickness can be formed by repeating thecoating and drying operations two to three times.

Boron nitride among the constituents demonstrates excellent lubricityparticularly at high temperatures. However, boron nitride as a singleconstituent is inferior in its adhesion onto the outer peripheralsurface of the preform in a manufacturing method which will be describedlater, and, hence, in its adhesion onto the surface of the partiallyconvex spherical portion of the seal in the compression process.Consequently, boron nitride as a single constituent has a drawback inthat it is easily exfoliated from the surface.

In the present invention, it was found that by compounding aluminaand/or silica with boron nitride at a fixed ratio, the aforementioneddrawback of boron nitride as a single constituent can be avoided, thatits adhesion onto the outer peripheral surface of the preform and,hence, its adhesion onto the partially convex spherical portion of theseal in the compression process can be improved substantially, that theretention of the lubricating sliding layer, formed by the lubricatingcomposition, on the surface of the partially convex spherical portion ofthe seal can be enhanced, and that the wear resistance of boron nitridecan be enhanced.

It was confirmed that the proportion in which alumina and/or silica iscompounded with respect to boron nitride is determined from theviewpoint of improving adhesion and wear resistance without impairingthe lubricity of boron nitride, and that a range of 10 to 30 wt. % istherefore preferable.

In the aforementioned lubricating composition in which the lubricatingcomposition containing 70 to 90 wt. % of boron nitride and 10 to 30 wt.% of alumina and/or silica is set as 100 parts by weight, and whichcontains polytetrafluoroethylene at a fixed ratio,polytetrafluoroethylene itself has a low frictional property, and as itis compounded with the lubricating composition formed of boron nitrideand alumina and/or silica, polytetrafluoroethylene exhibits the actionof improving a low frictional property of the lubricating composition,the action of enhancing the ductility of the lubricating compositionduring compression forming, and the action of improving the adhesion ofthe lubricating composition.

The proportion in which polytetrafluoroethylene is compounded withrespect to 100 parts by weight of the lubricating composition containing70 to 90 wt. % of boron nitride and 10 to 30 wt. % of alumina and/orsilica is 200 parts by weight or less, preferably in the range of 50 to150 parts by weight.

If the compounding proportion of polytetrafluoroethylene exceeds 200parts by weight, the proportion of the resin in the lubricatingcomposition becomes too large, with the result that the lubricity ofboron nitride, among the components, at high temperatures is impaired.If the compounding proportion of polytetrafluoroethylene is in the rangeof 50 to 150 parts by weight, the aforementioned actions can bedemonstrated most satisfactorily without impairing the lubricity ofboron nitride at high temperatures.

Graphite may be further compounded, in the proportion of 5 to 15 wt. %,in the lubricating composition including the above-described componentsfor the purpose of improving the wear resistance of the lubricatingsliding layer.

Boron nitride, alumina and/or silica as well as polytetrafluoroethylenefor forming the above-described aqueous dispersion are preferably in theform of as fine powders as possible, and fine powders having averageparticle sizes of 10 μm or less, preferably 1 μm or less, morepreferably 0.5 μm or less, are used.

Next, a description will be given of a method of manufacturing aspherical annular seal formed of the above-described constituentmaterials.

(First Method)

As shown in FIG. 4, a die 1 is prepared which has an inner cylindricalwall surface 11, a truncated conical inner wall surface 12, and athrough hole 13 continuing from the truncated conical inner wall surface12, a generally cylindrical hollow portion S being formed therein as astepped core 14 is fitted in the through hole 13.

A tubular woven metal mesh having mesh openings of 3 to 6 mm isfabricated by using fine metal wires having a diameter of 0.10 to 0.32mm. This tubular woven metal mesh is passed between pressure rollers soas to be formed into a sheet, and is then wound around an outerperipheral surface of the stepped core 14 by one turn, and anoverlapping portion is secured by means of spot welding, thereby forminga tubular reinforcing member 2. The tubular reinforcing member 2 isfitted over the outer peripheral surface of the stepped core 14 and isheld in the generally cylindrical hollow portion S of the die 1.

A mixture including metal short fibers, a solid lubricant, and asynthetic resin binder is filled in the cylindrical hollow portion S ofthe die 1 in such a manner as to cover the tubular reinforcing member 2held and fitted over the outer peripheral surface of the stepped core14, as shown in FIG. 5. The mixture and the reinforcing member aresubjected to compression forming under a pressure of 0.1 to 0.8 ton/cm²in the axial direction of the core, thereby forming a cylindricalpreform 3 having the tubular reinforcing member 2 integrated with themixture A on its inner surface, as shown in FIG. 6.

An aqueous dispersion containing as a solid content 20 to 50 wt. % of alubricating composition containing 70 to 90 wt. % of boron nitride and10 to 30 wt. % of alumina and/or silica, or an aqueous dispersioncontaining as a solid content 20 to 50 wt. % of a lubricatingcomposition in which a lubricating composition containing 70 to 90 wt. %of boron nitride and 10 to 30 wt. % of alumina and/or silica is set as100 parts by weight, and which additionally containspolytetrafluoroethylene in the proportion of 200 parts by weight orless, preferably 50 to 150 parts by weight, is coated on an outerperipheral surface of the preform 3, and is then dried. Thus, a coatinglayer B consisting of the lubricating composition is formed on the outerperipheral surface of the preform 3, as shown in FIG. 7.

As shown in FIG. 8, a die 4 is prepared which has a cylindrical innerwall surface 41, a partially concave spherical inner wall surface 42continuing from the cylindrical inner wall surface 41, and a throughhole 43 continuing from the partially concave spherical inner wallsurface 42, and in which a hollow cylindrical portion 45 and a sphericalannular hollow portion 46 continuing from the hollow cylindrical portion45 are formed inside it as a stepped core 44 is inserted in the throughhole 43.

The preform 3 with the coating layer B of the lubricating compositionformed on its outer peripheral surface is fitted over the stepped core44 of the die 4, and is subjected to compression forming under apressure of 1 to 3 tons/cm² in the direction of the core axis. Thus, aspherical annular member 5 is formed which has in its center a throughhole 51 with its inner peripheral surface reinforced by the compressedreinforcing member 2, and in which a sliding layer 6 constituted by thelubricating composition is formed on its outer partially convexspherical surface portion 52, as shown in FIG. 9.

By means of this compression forming, the coating layer B constituted bythe lubricating composition formed on the outer peripheral surface ofthe preform 3 is spread, and is formed on the outer partially convexspherical surface portion 52 as the lubricating sliding layer 6 having avery small thickness (10 to 300 μm).

The spherical annular member 5 thus obtained is placed in a heatingfurnace, which is heated to a predetermined temperature, for apredetermined time so as to heat and cure the synthetic resin binder inthe mixture constituting the member 5, thereby obtaining a finalspherical annular seal 7.

As shown in FIG. 1, the final spherical annular seal 7 has in its centera through hole 71 with its inner peripheral surface reinforced by thereinforcing member 2 constituted by the metal mesh as well as apartially convex spherical surface portion 72 on its outer surface, thelubricating sliding layer 6 being formed on the surface of the partiallyconvex spherical surface portion 72.

(Second Method)

By using a method similar to the above-described first method, thepreform 3 having the tubular reinforcing member 2 integrated with themixture A on its inner peripheral surface is formed, as shown in FIG. 6.Further, by using a method similar to that of the above-described firstmethod, the coating layer B constituted by the lubricating compositionis formed on the outer peripheral surface of the preform 3, as shown inFIG. 7.

A tubular reinforcing member 2A formed by weaving fine metal wires isprepared, and the preform 3 having the coating layer B is provided withthe tubular reinforcing member 2A on its outer peripheral surface insuch a manner as to cover the coating layer B. As shown in FIG. 10, thedie 4 similar to the one used in the above-described first method isprepared, and the preform 3 provided with the reinforcing member 2A onits outer peripheral surface in such a manner as to cover the coatinglayer B is fitted over the stepped core 44 of the die 4. The preform 3and the reinforcing member 2A are subjected to compression forming undera pressure of 1 to 3 ton/cm² in the direction of the core axis. Thus,the spherical annular member 5 is formed which has in its center thethrough hole 51 with its inner peripheral surface reinforced by thecompressed reinforcing member 2, and which has the outer partiallyconvex spherical surface portion 52 covered with a smooth surface inwhich the lubricating sliding layer 6 constituted by the lubricatingcomposition and the reinforcing member 2A are integrated in mixed form,as shown in FIG. 11.

By means of this compression forming, the coating layer B constituted bythe lubricating composition formed on the outer peripheral surface ofthe preform 3 is spread, and is formed on the outer partially convexspherical surface portion 52 as the lubricating sliding layer 6 having avery small thickness. At the same time, the lubricating sliding layer 6is integrated with the reinforcing member 2A as the reinforcing member2A compressed in conformity with the partially concave spherical innerwall surface 42 of the die 4 bites into the lubricating sliding layer 6.

The spherical annular member 5 thus obtained is placed in a heatingfurnace, which is heated to a predetermined temperature, for apredetermined time so as to heat and cure the synthetic resin binder inthe mixture constituting the member 5, thereby obtaining a finalspherical annular seal 7A.

As shown in FIG. 2, the final spherical annular seal 7A has in itscenter the through hole 71 with its inner peripheral surface reinforcedby the reinforcing member 2 formed of the metal mesh as well as thepartially convex spherical surface portion 72 on its outer surface, thesurface of the partially convex spherical surface portion 72 beingformed into a smooth surface in which the lubricating sliding layer 6and the reinforcing member 2A are integrated in mixed form.

(Third Method)

A mixture of the solid lubricant, the metal short fibers, and thesynthetic resin binder is filled in the cylindrical hollow portion S ofthe die 1, such as the one shown in FIG. 4. The mixture is subjected tocompression forming in the direction of the core axis, thereby forming apreform 3A.

An aqueous dispersion containing as a solid content 20 to 50 wt. % of alubricating composition containing 70 to 90 wt. % of boron nitride and10 to 30 wt. % of alumina and/or silica, or an aqueous dispersioncontaining as a solid content 20 to 50 wt. % of a lubricatingcomposition in which a lubricating composition containing 70 to 90 wt. %of boron nitride and 10 to 30 wt. % of alumina and/or silica is set as100 parts by weight, and which additionally containspolytetrafluoroethylene in the proportion of 200 parts by weight orless, preferably 50 to 150 parts by weight, is coated on an outerperipheral surface of the preform 3A, and is then dried. Thus, thecoating layer B consisting of the lubricating composition is formed onthe outer peripheral surface of the preform 3A.

A reinforcing member 2B, which is shown in FIG. 12 and is formed of ametal mesh having an inner tubular portion 21, a curved portion 22continuing from the inner tubular portion 21, and an outer tubularportion 23 continuing from the curved portion, is prepared. The preform3A on which the coating layer B constituted by the lubricatingcomposition is formed is inserted between the inner and outer tubularportions 21 and 23 of the reinforcing member 2B, as shown in FIG. 13.The die 4 similar to the one used in the above-described first method isprepared. This assembly of the preform 3A and reinforcing member 2B isfitted over the outer peripheral surface of the stepped core 44 of thedie 4 so as to be located in the spherical annular hollow portion 46.

The assembly is subjected to compression forming in the direction of thecore axis. Thus, a spherical annular member is formed which has in itscenter a through hole with its inner peripheral surface reinforced bythe compressing of the inner portion 21 of the reinforcing member 2B,and which has a partially convex spherical surface portion on its outersurface. The surface of the partially convex spherical surface portionis formed into such a smooth surface that the lubricating sliding layerconstituted by the lubricating composition and the reinforcing member 2Bextending from the through hole and covering a small-diameter end of thepartially convex spherical surface portion as well as the lubricatingsliding layer on the partially convex spherical surface portion areintegrated in mixed form. By means of this compression forming, thecoating layer B constituted by the lubricating composition formed on theouter peripheral surface of the preform 3 is spread, and is formed onthe outer partially convex spherical surface portion as the lubricatingsliding layer having a very small thickness. At the same time, thelubricating sliding layer is integrated with the reinforcing member 2Bas the outer tubular portion 23 of the reinforcing member 2B compressedin conformity with the partially concave spherical inner wall surface 42of the die 4 bites into the lubricating sliding layer.

The spherical annular member thus obtained is placed in a heatingfurnace, which is heated to a predetermined temperature, for apredetermined time so as to heat and cure the synthetic resin binder inthe mixture constituting the form, thereby obtaining a final sphericalannular seal 7B. As shown in FIG. 3, the final spherical annular seal 7Bhas in its center the through hole 71 with its inner peripheral surfacereinforced by the inner portion 21 of the reinforcing member 2Bconstituted by the metal mesh as well as the partially convex sphericalsurface portion 72 on its outer surface, the surface of the partiallyconvex spherical surface portion 72 being formed into a smooth surfacein which the lubricating sliding layer 6 and the outer portion 23 of thereinforcing member 2B are integrated in mixed form. In addition, thesmall-diameter end of the outer partially convex spherical surfaceportion of the spherical annular seal 7B is reinforced by the curvedportion 22 of the reinforcing member 2B.

Each of the spherical annular seals 7, 7A, and 7B constructed asdescribed above is used by being incorporated in an exhaust pipe jointshown in FIG. 14.

That is, a flange 200 is provided uprightly on an outer peripheralsurface of an upstream-side exhaust pipe 100, which is connected to anengine, with a pipe end 101 projecting from the flange 200 in thelongitudinal direction of the exhaust pipe 100. The spherical annularseal 7 (7A, 7B) is fitted over the pipe end 101 at the through hole 71,and is seated with a large-diameter-side end face of the partiallyconvex spherical surface portion 72 abutting against that flange 200.

A downstream-side exhaust pipe 300 opposes at one end the upstream-sideexhaust pipe 100 and is connected at the other end to a muffler. Aflared portion 301, which is comprised of a concave spherical surfaceportion 302 and a flange portion 303 provided at a rim of an openingportion of the concave spherical surface portion 302, is formedintegrally at one end of the downstream-side exhaust pipe 300. Theexhaust pipe 300 is disposed with the concave spherical surface portion302 slidingly abutting against the partially convex spherical surfaceportion 72 of the spherical annular seal 7.

The downstream-side exhaust pipe 300 is connected to the upstream-sideexhaust pipe 100 in such a manner as to be constantly urged toward theupstream-side exhaust pipe 100 by means of a pair of bolts 400 eachhaving one end fixed to the flange 200 and another end arranged by beinginserted in the flange portion 303 of the flared portion 301, and bymeans of a pair of coil springs 500 each arranged between a head of thebolt 400 and the flange portion 303.

The arrangement provided is such that relative angular displacementsoccurring in the upstream- and downstream-side exhaust pipes 100 and 300are allowed by sliding contact between the partially convex sphericalsurface portion 72 of the spherical annular seal 7 and the concavespherical surface portion 302 of the flared portion 301 formed at theend of the downstream-side exhaust pipe 300.

Hereafter, a detailed description will be given of examples of thespherical annular seal in accordance with the present invention.

Example I

By using graphite powder as the solid lubricant, the graphite powder,steel fibers having a diameter of 100 μm and a length of 500 μm, and aphenol resin binder were charged into a mixer and were stirred andmixed, thereby preparing a uniform mixture A of the graphite powder, thesteel short fibers, and the phenol resin binder (graphite: 22 wt. %,steel short fibers: 57 wt. %, and the phenol resin binder: 21 wt. %).

By using a stainless steel wire having a diameter of 0.3 mm as thereinforcing member, a tubular woven mesh having mesh openings of 5 mmwas fabricated. This tubular woven mesh was passed between pressurerollers into a sheet, and was then convoluted into a tubular shape, andan overlapping portion was secured by means of spot welding, therebyforming the tubular reinforcing member 2.

The aforementioned die 1 was prepared, and the reinforcing member 2 wasfitted over the outer peripheral surface of the core 14 so as to be heldin the generally cylindrical hollow portion S of the die 1.

Subsequently, the mixture was filled in the cylindrical hollow portion Sof the die in such a manner as to cover the reinforcing member 2 heldand fitted over the outer peripheral surface of the core 14, and themixture and the reinforcing member 2 were subjected to compressionforming under a pressure of 0.3 ton/cm² in the direction of the coreaxis, thereby fabricating a cylindrical preform having on its innersurface a reinforcing member integrated with the mixture.

An aqueous dispersion (its composition: 25.5 wt. % of boron nitride, 4.5wt. % of alumina, and 70 wt. % of water) containing as a solid content30 wt. % of a lubricating composition containing 85 wt. % of boronnitride powder with an average particle size of 7 μm and 15 wt. % ofalumina powder with an average particle size of 0.6 μm, was prepared andcoated on the outer peripheral surface of the preform, and was thendried. This operation of coating and drying was repeated three times toform a coating layer of the lubricating composition on the outerperipheral surface of the preform.

The aforementioned die 4 was prepared, and the preform provided with thecoating layer of the lubricating composition on its outer peripheralsurface was fitted over the stepped core 44 of the die 4, and wassubjected to compression forming under a pressure of 2.5 ton/cm² in thedirection of the core axis. Thus, the spherical annular member wasfabricated which had in its center a through hole with its innerperipheral surface reinforced by the compressed reinforcing member, andhad on its outer surface the partially convex spherical surface portion,a lubricating sliding layer of the lubricating composition containing 85wt. % of boron nitride and 15 wt. % of alumina being formed on thesurface of the partially convex spherical surface portion.

The spherical annular member thus obtained was preheated for 30 minutesin a heating furnace set at a temperature of 80° C., and was then heatedfor two hours at a temperature of 180° C. to cure the synthetic resinbinder in the mixture constituting the form, thereby obtaining aspherical annular seal.

Example II

By using the same die, tubular reinforcing member, and mixture as thoseof Example I above, a preform having the reinforcing member integratedwith the mixture on its inner surface was fabricated. An aqueousdispersion (17 wt. % of boron nitride, 3 wt. % of alumina, 10 wt. % ofpolytetrafluoroethylene, and 70 wt. % of water) containing as a solidcontent 30 wt. % of a lubricating composition (56.7 wt. % of boronnitride, 10 wt. % of alumina, and 33.3 wt. % of polytetrafluoroethylene)in which a lubricating composition containing 85 wt. % of boron nitridepowder with an average particle size of 7 μm and 15 wt. % of aluminapowder with an average particle size of 0.6 μm was set as 100 parts byweight, and which additionally contained 50 parts by weight ofpolytetrafluoroethylene powder with an average particle size of 0.3 μm,was prepared. This aqueous dispersion was coated on the outer peripheralsurface of the preform, and was then dried. This operation of coatingand drying was repeated three times to form the coating layer of thelubricating composition on the outer peripheral surface of the preform.

Thereafter, by using the same method as that of Example 1, a sphericalannular seal was obtained which had in its center a through hole withits inner peripheral surface reinforced by the compressed tubularreinforcing member, and had on its outer surface the partially convexspherical surface portion, a lubricating sliding layer of thelubricating composition containing 56.7 wt. % of boron nitride, 10 wt. %of alumina, and 33.3 wt. % of polytetrafluoroethylene being formed onthe surface of the partially convex spherical surface portion.

Example III

By using the same mixture as that of the above-described Example I, apreform constituted by the mixture was prepared. An aqueous dispersionsimilar to that of the above-described Example II was coated on theouter peripheral surface of this preform, and was then dried. Thisoperation of coating and drying was repeated three times to form thecoating layer of the lubricating composition on the outer peripheralsurface of the preform.

As the reinforcing member, by using a stainless steel wire having adiameter of 0.3 mm, a tubular woven mesh having mesh openings of 5 mmwas fabricated. After this tubular woven mesh was cut into apredetermined length, one end of the mesh was turned back toward theother end, thereby forming a reinforcing member comprised of an innertubular portion, a turned-back curved portion continuing from the innertubular portion, and an outer tubular portion continuing from the curvedportion. The preform having the coating layer of the aforementionedlubricating composition was inserted between the inner and outer tubularportions of this reinforcing member, thereby fabricating an assembly ofthe reinforcing member and the preform.

Subsequently, a die similar to that used in Example I was prepared, andthe assembly of the reinforcing member and the preform was fitted overthe outer peripheral surface of the stepped core of the die, was locatedin the spherical annular hollow portion of the die, and was subjected tocompression forming in the direction of the core axis. Thus, a sphericalannular member was formed which had in its center a through hole withits inner peripheral surface reinforced by the compressing of the innertubular portion of the reinforcing member, and which had a partiallyconvex spherical surface portion on its outer surface. The surface ofthe partially convex spherical surface portion was formed into such asmooth surface that the lubricating sliding layer constituted by thelubricating composition and the reinforcing member 2B extending from thethrough hole and covering a small-diameter end of the partially convexspherical surface portion as well as the lubricating sliding layer onthe partially convex spherical surface portion were integrated in mixedform.

The spherical annular member thus obtained was preheated for 30 minutesin a heating furnace set at a temperature of 80° C., and was then heatedfor two hours at a temperature of 180° C. to cure the synthetic resinbinder in the mixture constituting the form, thereby obtaining aspherical annular seal.

Comparative Example

A cylindrical preform having a tubular reinforcing member integratedwith the mixture A on its inner surface was fabricated by a methodsimilar to that of the above-described Example I.

An aqueous dispersion (15 wt. % of polytetrafluoroethylene, 6 wt. % ofgraphite, 6 wt. % of tungsten disulfide, 3 wt. % of calcium fluoride,and 70 wt. % of water) containing as a solid content 30 wt. % of alubricating composition including 50 wt. % of polytetrafluoroethylenepowder with an average particle size of 0.3 μm, 20 wt. % of graphitepowder, 20 wt. % of tungsten disulfide powder, and 10 wt. % of calciumfluoride powder, was prepared. This aqueous dispersion was coated on theouter peripheral surface of the preform, and was dried, thereby forminga coating layer of the lubricating composition on the outer surface ofthe preform.

Thereafter, in a method similar to that of Example I, a sphericalannular seal was obtained which had in its center a through hole withits inner peripheral surface reinforced by the compressed reinforcingmember, and had on its outer surface the partially convex sphericalsurface portion, a lubricating sliding layer of the lubricatingcomposition containing 50 wt. % of polytetrafluoroethylene, 20 wt. % ofgraphite, 20 wt. % of tungsten disulfide, and 10 wt. % of calciumfluoride being formed on the surface of the partially convex sphericalsurface portion.

Then, with respect to the spherical annular seals in accordance with theabove-described Examples and Comparative Example, tests were conductedfor measurement of a frictional torque (kgf. cm) during an initialperiod of friction of the seals and for checking the presence or absenceof the occurrence of abnormal noise by using the exhaust pipe jointshown in FIG. 14, and its results are discussed below.

(Test I)

Test Conditions:

Pressing force using coil springs: 60 kgf

Angle of oscillation: ±3°

Frequency: 10 hertz

Ambient temperature (temperature of the outer surface temperature of theconcave spherical surface portion 302 shown in FIG. 14): from roomtemperature (20° C.) to 500° C.

Test Method: An oscillating motion at ±3° at a frequency of 10 hertz isset as a unit of oscillation, and is performed 45,000 times at roomtemperature. The ambient temperature is then raised to 500° C. whilecontinuing the oscillating motion (the number of oscillating motionsduring the temperature rise being 45,000). When the ambient temperaturereaches 500° C., the oscillating motion is performed 115,000 times.Finally, the temperature is allowed to drop to room temperature whilecontinuing the oscillating motion (the number of oscillating motionsduring the temperature drop being 45,000). The total number ofoscillating motions of 250,000 is set as one cycle, and four cycles areperformed.

(Test II)

Test Conditions:

Pressing force using coil springs: 72 kgf

Angle of oscillation: ±3°, ±2° (two directions that are perpendicular toeach other; in FIG. 14, a direction perpendicular to the axes of thebolts is set as an X-direction, while a direction perpendicular to theX-direction is set as a Y-direction)

Frequency: 1.6 hertz, 12 hertz (X-direction), 7.2 hertz (Y-direction)

Ambient temperature (temperature of the outer surface temperature of theconcave spherical surface portion 302 shown in FIG. 14): from roomtemperature (20° C.) to 500° C.

Test Method: An oscillating motion at ±3° in the X-direction is set as aunit of oscillation, and the oscillating motion at a frequency of 1.6hertz is performed 1000 times at room temperature. The ambienttemperature is then raised to 500° C. while continuing the oscillatingmotion (the number of oscillating motions during the temperature risebeing 5000). When the ambient temperature reaches 500° C., theoscillating motion in the X-direction is increased to 12 hertz, and isperformed 44,000 times. Also, with respect to the Y-directionperpendicular to the X-direction, an oscillating motion at a frequencyof 7.2 hertz and ±2° is set as a unit of oscillation, and theoscillating motion is performed 26,400 times. Subsequently, theoscillating conditions only with respect to the X-direction are changedto the oscillating motion at 1.6 hertz and ±3°, the oscillating motionin the Y-direction is stopped, and the temperature is allowed to drop toroom temperature (the number of oscillating motions during thetemperature drop being 500). The total number of oscillating motions of55,000 in the X-direction and the total number of oscillating motions of26,400 in the Y-direction are set as one cycle, and four cycles areperformed.

In addition, the evaluation of the presence or absence of the occurrenceof abnormal noise is conducted as follows.

Evaluation Code I: No abnormal noise occurred.

Evaluation Code II: Abnormal noise is heard slightly with the earbrought close to the test piece.

Evaluation Code III: Although the noise is generally difficult todiscern at a fixed position (a position 1.5 m distant from the testpiece) since it is blanketed by the noises of the living environment,the noise can be discerned as abnormal noise by a person in charge ofthe test.

Evaluation Code IV: The noise can be recognized as abnormal noise(unpleasant sound) by anybody at the fixed position.

Table 1 shows the results of the above-described Test I.

                  TABLE 1                                                         ______________________________________                                                 Example                                                                              Example  Example  Comparative                                          I      II       III      Example                                     ______________________________________                                        1    Frictional                                                                               70-100  60-80  60-80  60-90                                        torque                                                                        Abnormal  I        I      I      I                                            noise                                                                    2    Frictional                                                                              100-120   90-100                                                                               90-100                                                                               90-100                                      torque                                                                        Abnormal  I        I      I      I                                            noise                                                                    3    Frictional                                                                              110-130  100-110                                                                              100-110                                                                              100-130                                      torque                                                                        Abnormal  I        I      I      I                                            noise                                                                    4    Frictional                                                                              110-130  100-120                                                                              100-120                                                                              100-130                                      torque                                                                        Abnormal  I        I      I      I                                            noise                                                                    ______________________________________                                    

In Table 1, item 1 represents the results with the number of oscillatingmotions of 0 to 250,000; item 2 represents the results with the numberof oscillating motions of 250,000 to 500,000; item 3 represents theresults with the number of oscillating motions of 500,000 to 750,000;and item 4 represents the results with the number of oscillating motionsof 750,000 to 1,000,000.

From these test results, no difference in performance is recognizedbetween the Examples and the Comparative Example, the frictional torqueis low in both cases, and no occurrence of abnormal noise is recognized.Table 2 shows results of the above-described Test II.

                  TABLE 2                                                         ______________________________________                                                 Example                                                                              Example  Example  Comparative                                          I      II       III      Example                                     ______________________________________                                        1    Frictional                                                                               70-100  60-80  60-80  60-90                                        torque                                                                        Abnormal  I        I      I      II                                           noise                                                                    2    Frictional                                                                               70-120  50-100 50-100 50-100                                       torque                                                                        Abnormal  II       II     I      IV                                           noise                                                                    3    Frictional                                                                              100-120  50-100 50-100 80-130                                       torque                                                                        Abnormal  I        I      I      I                                            noise                                                                    4    Frictional                                                                              100-120  50-100 50-100 80-130                                       torque                                                                        Abnormal  I        I      I      I                                            noise                                                                    ______________________________________                                    

In Table 2, item 1 shows the results with the number of oscillatingmotions of 0 to 55,000 in the X-direction (the number of oscillatingmotions in the Y-direction being 26,400); item 2 represents the resultswith the number of oscillating motions of 55,000 to 110,000 (the numberof oscillating motions in the Y-direction being 52,800); item 3represents the results with the number of oscillating motions of 110,000to 165,000 (the number of oscillating motions in the Y-direction being79,200); and item 4 represents the results with the number ofoscillating motions of 165,000 to 220,000 (the number of oscillatingmotions in the Y-direction being 105,600).

From the test results, stable performance is noted for the sphericalannular seal in accordance with the Example throughout the test periodwithout occurrence of abnormal noise.

Meanwhile, in the case of the spherical annular seal of the ComparativeExample, the occurrence of slight abnormal noise is recognized up to thenumber of oscillating motions of 55,000 in the X-direction (the numberof oscillating motions in the Y-direction being 26,400). Furthermore,the occurrence of unpleasant abnormal noise is recognized in the rangeof the number of oscillating motions of 55,000 to 110,000 (the number ofoscillating motions in the Y-direction being 52,800). However, theoccurrence of abnormal noise is not recognized at a level exceeding thenumber of oscillating motions of 110,000.

The occurrence of unpleasant abnormal noise in the range of the numberof oscillating motions of 55,000 to 110,000 is presumably recognized ina state in which the lubricating sliding layer of the lubricatingcomposition formed on the surface has exfoliated, and the friction witha mating member has shifted to friction with the mixture on thepartially convex spherical surface portion on which the lubricatingsliding layer is formed.

Then, due to the subsequent friction, a coating of the solid lubricant(graphite) in the mixture is formed on the surface of the mating member,and the friction shifted to friction with that coating, with the resultthat the occurrence of unpleasant noise (abnormal noise) ceased.

From the above-described Tests I and II, it can be appreciated that theseal in accordance with the Example exhibits stable performance withoutoccurrence of abnormal noise irrespective of the conditions in which theseal is used.

Although examples in which alumina is used have been shown in theabove-described embodiment, silica may be used instead of alumina, orboth alumina and silica may be used, in which cases it is possible toobtain advantages similar to those obtained in the examples.

What is claimed is:
 1. A method of manufacturing a spherical annularseal, comprising the steps of:(1) fitting a tubular reinforcing memberformed of a metal mesh over an outer peripheral surface of a core of adie having a generally cylindrical hollow portion in its interior; (2)forming a preform having said reinforcing member integral in and on itsinner surface by filling a mixture of a solid lubricant, metal shortfibers, and a synthetic resin binder in the hollow portion in such amanner as to fill in mesh openings of said reinforcing member and coversaid reinforcing member, and by compression forming said mixture andsaid reinforcing member in a direction of a core axis; (3) forming acoating layer constituted by a lubricating composition by coating anouter peripheral surface of said preform with an aqueous dispersioncontaining as a solid content 20 to 50 wt. % of said lubricatingcomposition containing 70 to 90 wt. % of boron nitride and 10 to 30 wt.% of alumina and/or silica, and by drying said aqueous dispersion; (4)preparing a die having a partially concave spherical surface portion onits inner surface, and fitting said preform with said coating layer ofsaid lubricating composition formed thereon over an outer peripheralsurface of said core of said die; (5) compressing said preform in adirection of a core axis for obtaining a spherical annular member whichhas in its center a through hole with its inner peripheral surfacereinforced by the compressed reinforcing member, as well as a partiallyconvex spherical surface portion on its outer surface, a uniformlubricating sliding layer of said lubricating composition containing 70to 90 wt. % of boron nitride and 10 to 30 wt. % of alumina and/or silicabeing formed on a surface of said partially convex spherical surfaceportion; and (6) placing said spherical annular member in a heatingfurnace to heat and cure said synthetic resin binder in said mixture andheating curing said synthetic resin binder.
 2. A method of manufacturinga spherical annular seal, comprising the steps of:(1) fitting a tubularreinforcing member formed of a metal mesh over an outer peripheralsurface of a core of a die having a generally cylindrical hollow portionin its interior; (2) forming a preform having said reinforcing memberintegral in and on its inner surface by filling a mixture of a solidlubricant, metal short fibers, and a synthetic resin binder in thehollow portion in such a manner as to fill in mesh openings of saidreinforcing member and cover said reinforcing member, and by compressionforming said mixture and said reinforcing member in a direction of acore axis; (3) forming a coating layer constituted by a lubricatingcomposition by coating an outer peripheral surface of said preform withan aqueous dispersion containing as a solid content 20 to 50 wt. % ofsaid lubricating composition containing 70 to 90 wt. % of boron nitrideand 10 to 30 wt. % of alumina and/or silica, and by drying said aqueousdispersion; (4) preparing a die having a partially concave sphericalsurface portion on its inner surface, and fitting said preform with saidcoating layer of said lubricating composition formed thereon over anouter peripheral surface of said core of said die, and fitting a tubularreinforcing member formed of a metal mesh over an outer peripheralsurface of said preform; (5) compressing said preform and saidreinforcing member in a direction of a core axis for obtaining aspherical annular member which has in its center a through hole with itsinner peripheral surface reinforced by the compressed reinforcingmember, as well as a partially convex spherical surface portion on itsouter surface, a surface of said partially convex spherical surfaceportion being formed into a smooth surface in which a lubricatingsliding layer of said lubricating composition containing 70 to 90 wt. %of boron nitride and 10 to 30 wt. % of alumina and/or silica and saidreinforcing member formed of said metal mesh covering said lubricatingsliding layer and integrated with said lubricating sliding layer arepresent in mixed form; and (6) placing said spherical annular member ina heating furnace to heat and cure said synthetic resin binder in saidmixture and heating curing said synthetic resin binder.
 3. A method ofmanufacturing a spherical annular seal, comprising the steps of:(1)preparing a die having a generally cylindrical hollow portion in itsinterior by filling a mixture of a solid lubricant, metal short fibers,and a synthetic resin binder in said hollow portion, and compressionforming said mixture in a direction of a core axis so as to form apreform; (2) forming a coating layer constituted by a lubricatingcomposition by coating an outer peripheral surface of said preform withan aqueous dispersion containing as a solid content 20 to 50 wt. % ofsaid lubricating composition containing 70 to 90 wt. % of boron nitrideand 10 to 30 wt. % of alumina and/or silica, and by drying said aqueousdispersion; (3) preparing a reinforcing member formed of a metal meshhaving an inner tubular portion, a curved portion continuing from saidinner tubular portion, and an outer tubular portion continuing from saidcurved portion; (4) inserting said preform with said coating layer ofsaid lubricating composition formed thereon between said inner and outertubular portions of said reinforcing member formed of said metal mesh,and fitting an assembly of said preform and said reinforcing member overan outer peripheral surface of a core of a die having a partiallyconcave spherical surface portion on its inner surface so as to belocated on said partially concave spherical surface portion of said die;(5) compression forming the assembly in a direction of a core axis, forobtaining a spherical annular member which has in its center a throughhole with its inner peripheral surface reinforced by the compressedreinforcing member, as well as a partially convex spherical surfaceportion on its outer surface, a surface of said partially convexspherical surface portion being formed into a smooth surface in which alubricating sliding layer of said lubricating composition containing 70to 90 wt. % of boron nitride and 10 to 30 wt. % of alumina and/or silicaand said reinforcing member integrated with said lubricating slidinglayer in such a manner as to extend from the through hole and cover asmall-diameter end of said partially convex spherical surface portionand said lubricating sliding layer on said partially convex sphericalsurface portion are present in mixed form; and (6) placing saidspherical annular member in a heating furnace to heat and cure saidsynthetic resin binder in said mixture and heating curing said syntheticresin binder.
 4. The method of manufacturing a spherical annular sealaccording to wherein said lubricating composition contains 100 parts byweight of the lubricating composition containing 70 to 90 wt. % of boronnitride and 10 to 30 wt. % of alumina and/or silica, and furthercontains polytetrafluoroethylene in a proportion of not more than 200parts by weight.
 5. The method of manufacturing a spherical annular sealaccording to wherein said lubricating composition contains 100 parts byweight of the lubricating composition containing 70 to 90 wt. % of boronnitride and 10 to 30 wt. % of alumina and/or silica, and furthercontains polytetrafluoroethylene in a proportion ranging from 50 to 150parts by weight.
 6. The method of manufacturing a spherical annular sealaccording to claim 1 or 3, wherein said mixture includes 15 to 30 wt. %of said solid lubricant, 50 to 75 wt. % of said metal short fibers, and5 to 25 wt. % of said synthetic resin binder.
 7. The method ofmanufacturing a spherical annular seal according to claim 1 or 3,wherein said metal short fibers have a diameter of 10 to 200 μm and alength of 100 to 800 μm.
 8. The method of manufacturing a sphericalannular seal according to claim 1 or 3, wherein said reinforcing memberformed of said metal mesh is formed of said metal mesh obtained byweaving or knitting fine metal wires.